Conventionally, in the treating process of exhaust gas generated in manufacturing process of semiconductors and the like, exhaust gas treating apparatuses using a plasma are proposed and put in practical use (see, for example, patent document 1).
In this exhaust gas treating apparatus, the method for enhancing the decomposition efficiency of the exhaust gas to be treated includes: (1) a method of extending the plasma length (the discharge distance), (2) a method of reducing the diameter of the reaction tube for feeding the exhaust gas, and (3) a method of inducing a vortex flow by feeding an exhaust gas into the reaction tube from the tangential direction.
However, (1) the method of extending the plasma length (the discharge distance) is intended to raise the treating capacity, and is enhanced in the treating efficiency, but is increased in the energy consumption.
(2) The method of reducing the diameter of the reaction tube for feeding the exhaust gas is raised in the treating efficiency because the contact efficiency between the plasma and the exhaust gas is increased, but is decreased in the absolute amount of treating, and moreover since the tube wall of the reaction tube and the plasma are close to each other, the reaction tube is likely to be damaged, and there was a problem in the aspect of durability of the apparatus.
(3) The method of feeding an exhaust gas into the reaction tube from the tangential direction is higher in the treating efficiency because the contact efficiency between the plasma and the exhaust gas is increased, but is complicated in the structure of the feeding unit of exhaust gas of the reaction tube.